Me and my wife are playing 2 different games in AC Valhalla, each one with a different save, but sometimes when I try to load my save after she saved hers, I find myself reloading her save each time (even if I chose my save, a different number). One time also her save got rewritten by my save automatically (I use save 2, her is save 1, she load her save 1 and get stuck in my save 2. She close the game and at the new opening she find that her save 1 is identical to my save 2)

Same here, PS4 with 1.0.2... strange thing is that I've been able to do it with the 1.0.2 and my wife (same game, other save game) not...
We'll try to start a new game without downgrading and we'll see...